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Free keywords:
porphyrin, crystal structure, planar
macrocycle, fourfold symmetry, copper(II),
synchrotron
Abstract:
Porphyrin assemblies display interesting photophysical properties and a
relatively high thermal stability. Moreover, meso-functionalized porphyrins
with virtually fourfold symmetry can be relatively readily synthesized from
pyrrole and the appropriate aldehyde. A number of metallo derivatives of
5,10,15,20-tetrakis(4-cyanophenyl)porphyrin, where the N atom of the linear
cyano group can act both as a donor for coordination bonds or as an acceptor for
hydrogen bonds, have been structurally characterized by single-crystal
X-ray analysis. The supramolecular and structural chemistry of the corresponding
2- and 3-cyanophenyl isomers of the parent porphyrin, however, has
remained largely unexplored. The crystal structure of [5,10,15,20-tetrakis(3-
cyanophenyl)porphyrinato]copper(II) (CuTCNPP) nitrobenzene trisolvate,
[Cu(C48H24N8)]3C6H5NO2, has been determined at 80 K by synchrotron
single-crystal X-ray diffraction. CuTCNPP exhibits a C2h-symmetric [alpha][alpha][beta][beta]
conformation, despite an unsymmetrical crystal environment, and is situated
on a crystallographic centre of symmetry. The CuII ion adopts a genuine
square-planar coordination by the four pyrrole N atoms. The 24-membered
porphyrin ring system shows no marked deviation from planarity. In the
crystal, the CuTCNPP molecules and two nitrobenzene molecules are face-toface
stacked in an alternating fashion, resulting in corrugated layers. The
remaining nitrobenzene guest molecule per CuTCNPP resides in the region
between four neighbouring columnar stacks of CuTCNPP and sandwiched
nitrobenzene molecules, and is disordered over four positions about a centre of
symmetry.
